For now I am using a work around.

I use the robot class after I hide the borders. I show the image and send the robot keypress for ALT+PRINT SCREEN

It's crude but it works. I have to modify it so I can open a second offscreen window and size that to whatever size I want.
To be tested of course.

However the below code works [locally] The robot class only works with signed applications.

Run the script and open mspaint and paste. You will get a red box / window.

1. public Robot robot;
   PImage img;
   void init()
   {
     frame.removeNotify();
     frame.setUndecorated(true);
     frame.addNotify();
     super.init();
   }
   
   void setup()
   {
     colorMode(RGB,255);
   
     loadPixels();
     textureMode(NORMALIZED);
     frameRate(30);
     size(255,255,P3D);    //OPENGL does not display correctly
   
   
   
     textureMode(NORMALIZED);
     try
     {
   
       robot = new Robot();
       //BufferedImage bufferedImage = robot.createScreenCapture(
       //new Rectangle(new Dimension(screen.width, screen.height)));
   
       //img   = new PImage(bufferedImage);
   
   
     }
     catch (AWTException e) {
       e.printStackTrace();
     }
     background(255,0,0);
   }
   
   boolean firstrun = true;
   void draw(){
     if(firstrun){
       robot.keyPress(18);
       robot.keyPress(154);
       robot.keyRelease(18); // <<Important
       robot.keyRelease(154);// <<Important
     }
     firstrun = false;
     exit();
   }
   
   
   

I had a "copy from clipboard" experiment, I just added a "copy image to clipboard" part (found on the Net, adapted to Processing).
http://bazaar.launchpad.net/~philho/+junk/Processing/view/head:/_QuickExperiments/_Java/ClipboardManagement/ClipboardManagement.pde